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A
The Horizontal component becomes so weak that the directive force is insufficient for a reliable compass indication.
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B
The influence of the abundant local magnetic anomalies caused by ionised particles in the vicinity of the magnetic poles.
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C
The influence of Aurora Borealis (northern Lights) tends to deflect the compass.
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D
The decrease of the earth's magnetic field strength causes the directive force to be not sufficient for a reliable compass indication.
Refer to figure.
A freely suspended magnet will align itself with the Earth's magnetic field. The total field (T) is resolved into a horizontal component (H) and a vertical component (Z).
HORIZONTAL COMPONENT
The horizontal component is the part which is detected by the compass needle in order to determine Magnetic North. A compass is freely suspended in the horizontal plane and the needle will align itself with the Earth's horizontal component (H) of the Earth's magnetic field.
- The compass is ineffective near the poles. As you approach the poles, the angle between magnetic flux and the horizon becomes vertical – compass ‘dip’ becomes a factor => decrease in horizontal magnetic field, increase in vertical magnetic field.
- The value of the horizontal component is maximum at the Magnetic Equator, a freely suspended compass needle in the Earth's magnetic field will be horizontal to the Earth - in line with the horizontal component.
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This question has appeared on the real examination, you can find the related countries below.
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Austro Control2
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Lithuania1